Recently, a focus has been placed on a touch detection device, a so-called touch panel, which is capable of detecting an external proximity object. The touch panel is provided as a touch detection function-equipped display device in the state of being mounted on a display device, for example, a liquid crystal display device, or being integrated with the liquid crystal display device.
The external proximity object includes, for example, a touch panel which allows a pen to be used. By allowing the pen to be used, for example, it is possible to designate a small area or input a handwritten letter. There are various types of techniques to detect touch by the pen. One of the various types of techniques is an electromagnetic induction system. This electromagnetic induction system can realize a high accuracy and a high writing pressure detection accuracy, also realize a hovering detection function in which the external proximity object is spaced apart from a touch panel surface, and so is an effective technique as the technique of detecting the touch by the pen.
In addition, there is also a touch panel which allows a finger to be used as the external proximity object. It is unnecessary to prepare a pen or the like when it is possible to use the finger, which allows simplicity and convenience. For example, various button images and the like are displayed on a touch detection function-equipped display device, and the proximity of the finger to the button image is detected by the touch panel. Accordingly, it is possible to use the touch panel instead of a general mechanical button. Such a touch detection function-equipped display device does not necessarily require an information input means such as a keyboard and a mouse, and so tends to be widely used in portable information terminals or the like such as a mobile phone as well as a computer.
There are also various types of tecnique to detect the touch by the finger. For example, there are several systems such as an optical type, a resistance type, and a capacitance system. Among them, the capacitive system has a relatively simple structure, consumes low power, and so has been used in a portable information terminal or the like.
The touch panel that allows the use of the finger is simple and convenient, but it is not easy to designate a small area using the finger, for example. Thus, desired is a touch panel which allows both a pen and a finger to be used.
Touch detection techniques using the electromagnetic induction system are described in, for example, Japanese Patent Application Laid-open No. 10-49301 (Patent Document 1), Japanese Patent Application Laid-open No. 2005-352572 (Patent Document 2), and Japanese Patent Application Laid-open No. 2006-163745 (Patent Document 3).